My sleep 'schedule' is something like this, in practice. I go to sleep when I'm tired and get up when I wake up and am no longer tired, without worrying about the clock at all, and I've been doing so for 2 years now. My days usually last between 23 and 28 hours, and seem to run longer, not shorter, when I'm stressed or busy, both in terms of the length of time from the start of one sleep to the start of the next and in terms of the awake:asleep ratio.